This invention relates in general to apparatus for fusing toner images to copy sheets in electrographic apparatus and more particularly this invention relates to roller fuser apparatus in which the severity of copy sheet jams are minimized by means of rapid detection of fuser jams and rapid deactuation of the fuser in response to such jam detection.
Electrographic copiers are commonly used to produce copies of original documents. The reproduced copies comprise toner images of the original which are permanently affixed to copy sheets by well known fusing techniques. One such technique consists of passing a copy sheet having toner images on one or both sides thereof through the nip of a pair of rollers, one or both of which are heated to permanently fuse the toner image(s) to the copy sheet through the application of heat and pressure. Roller fusers are complex and compact structures which include several interdependent elements to insure proper functioning of the roller fuser. Thus, in addition to the support structure for the fuser rollers and the rollers themselves, the following elements are usually incorporated into a fuser roller: (1) A heat source for heating one or both of the fuser rollers. Generally, either quartz lamps are inserted inside the fuser rollers or a heating element applies heat to the external surface of the fuser rollers. (2) Applicators for applying fuser release material such as silicone fuser oil to the surfaces of either or both fuser rollers in order to minimize or eliminate offset of toner from fused copy sheets to the rollers and to aid in releasing the copy sheet from the roller surfaces. (3) Sensors positioned close to the surface of either or both of the rollers to monitor the heat level of the fuser rollers in order to maintain the temperature within predetermined limits and also to signal overheating so that the fuser roller may be shut down. (4) An enclosure in order to confine the heat from the fuser within the environs thereof to maintain efficient heating and to prevent heat from passing into the environment of the electrophotographic copier to degrade other components within the copier. (5) Copy sheet transport devices both in the inlet and outlet of the nip of the fuser roller; and (6) Skive elements at the roller nip exit to assist in stripping copy sheets from the fuser rollers. Since a high temperature resistant elastomeric material such as silicone rubber is commonly used as a fusing layer, it is advisable to provide a mechanism for engaging and disengaging the fuser rollers when not in use in order to prevent undesirable permanent set of the elastomeric material during nonuse of the copier.
Although roller fusers used in commercial electrographic copiers are so designed that copy sheets are routinely passed through the nip of the fuser roller, due to the dynamics of high-speed copiers and the tendency of heated copy sheets to adhere to fuser rollers during the fusing operation, jamming of copy sheets in the roller fuser does occur. Copy sheet jams are undesirable for a number of reasons. First, a copy sheet jam normally triggers a shutdown of the copier in order to prevent permanent damage to components of the copier. Second, in high-speed copiers, the response time to stop feeding copy sheets into the fuser is usually not short enough to prevent the feeding of two or three copy sheets into the roller fuser before shut down of copier operations. Due to the crowded nature of the elements of the fuser mechanism, the jamming together of two or three copy sheets into such a mechanism makes it difficult for an operator to clear jams easily and safely so that normal copier operation can be resumed. Moreover, during multiple sheet jams exit skives may be bent and driven into the fuser rollers, thus necessitating replacement of the skives and fuser rollers.
Since the trend in copier duplicators is to higher and higher copy output and to the production of duplex as well as simplex copies, roller fusers have become more complex and compact, thus exacerbating the difficulties caused by fuser jams. It is thus desirable to provide a roller fuser in electrographic copiers which may be deactuated rapidly in case of a jam so that at most only one copy sheet is jammed in the fuser. It is also desirable that provision be made for the easy and safe removal of a jammed copy sheet from the roller fuser and that any jammed copy sheet not cause permanent damage to the elements of the fuser. Limitation of copy sheet jams to a single sheet also permits faster recovery of copier operation.